The VDR gene encodes the vitamin D receptor, and its FokI, BsmI, ApaI and TaqI polymorphisms are the most widely reported vitamin D variants in consumer DNA data. They are also the basis for a great deal of genotype-specific dosing advice — which is where the evidence stops supporting the practice. In the largest study to test them, involving 26,242 participants, these four polymorphisms were not associated with bone mineral density or with fractures.
So the honest answer to "what dose does my VDR genotype call for?" is that these variants do not tell you. What does tell you is your measured blood 25(OH)D level, which is cheap to test, responds to supplementation, and is the number clinical recommendations are actually built on.
Check your own VDR: upload your 23andMe or AncestryDNA raw data to AskMyDNA and see which VDR variants you carry — and what they do and do not predict. Your first question is free, no credit card.
What the VDR Gene Actually Does
The VDR gene sits on chromosome 12 and encodes the vitamin D receptor — a nuclear receptor that, once bound by the active hormone calcitriol, regulates the transcription of a large set of target genes involved in calcium handling, bone remodelling, and immune function.
That much is solid, well-characterized biology, and it is why VDR looked like such a promising candidate gene in the first place. Vitamin D3 from sun or supplements is hydroxylated in the liver to 25(OH)D — the storage form measured in blood tests — and again in the kidney to the active hormone, which then acts through VDR.
The gap between "this receptor is essential" and "variants in this receptor predict your dose" is where the popular story overreaches. A receptor can be indispensable while its common variants explain almost nothing about differences between healthy people.
The Four Famous Polymorphisms — and What the Largest Study Found
FokI (rs2228570), BsmI (rs1544410), ApaI (rs7975232) and TaqI (rs731236) have been studied for decades. FokI is the one with a clear molecular story: it alters a start codon, producing a receptor protein of either 424 or 427 amino acids. BsmI, ApaI and TaqI sit near the 3' end of the gene and do not change the protein sequence at all.
The decisive test came from the Genetic Markers for Osteoporosis consortium — a prospective study across nine European research teams, pooling 26,242 participants and analysing individual-level data rather than published summaries. It examined exactly these polymorphisms against bone mineral density at the femoral neck and lumbar spine, and against fractures.
The results were flatly negative:
- Bone mineral density differences between genotypes were less than 0.011 g/cm² and non-significant, with or without adjustment.
- Across 6,067 participants with a fracture history and 2,088 with vertebral fractures, odds ratios for all VDR alleles were very close to 1.00 (range 0.98 to 1.02), with confidence intervals spanning 0.94 to 1.07.
The authors' conclusion is unambiguous: the FokI, BsmI, ApaI and TaqI VDR polymorphisms are not associated with bone mineral density or with fractures.
One partial exception is worth reporting accurately, because it is the only positive signal in the study. A fifth variant, the Cdx2 promoter polymorphism, showed a 9% reduction in vertebral fracture risk for the A allele — but with a 95% confidence interval running from 0% to 18% and P = 0.039, it sits right at the boundary of significance. That is a finding worth further study, not a basis for a supplement protocol, and Cdx2 is not among the variants dosing schemes are usually built on anyway.
From the peer-reviewed literature
"The FokI, BsmI, ApaI, and TaqI VDR polymorphisms are not associated with BMD or with fractures, but the Cdx2 polymorphism may be associated with risk for vertebral fractures."
— Uitterlinden AG et al., Genetic Markers for Osteoporosis consortium. The association between common vitamin D receptor gene variations and osteoporosis: a participant-level meta-analysis. Ann Intern Med. 2006. doi:10.7326/0003-4819-145-4-200608150-00005
Why the Older Literature Looked So Promising
If these variants do nothing, why are there hundreds of papers suggesting they do? The pattern is a familiar one in genetics. Early candidate-gene studies were small, and small studies produce scattered results — some positive by chance, and those are disproportionately the ones that get published and cited. Once sample sizes reached the tens of thousands and individual-level data could be pooled, the effect shrank toward zero.
This is the same arc that played out across most candidate-gene research from the same era. It is not a reason to distrust genetics; it is the reason large studies exist.
What Genetics Does Explain: Your Blood Level, Not Your Dose
Genetics has not been eliminated from the vitamin D picture. It has been relocated — away from the receptor and toward the enzymes and transport proteins that determine how much 25(OH)D circulates in the first place.
A genome-wide association study of 79,366 European-ancestry individuals identified loci influencing 25(OH)D concentrations, clustering around genes with clear mechanistic roles: GC (vitamin D binding protein, which carries the hormone in blood), CYP2R1 (the liver enzyme performing the first hydroxylation), DHCR7 (which governs the skin precursor available for UVB conversion), and CYP24A1 (which catabolizes vitamin D metabolites).
Randomized evidence points the same way. In a trial of 1,787 participants receiving 1,000 IU/day of vitamin D3 or placebo for a year, the increase in 25(OH)D attributable to supplementation was modified by genotypes near CYP2R1, CYP24A1 and VDR.
From the peer-reviewed literature
"The increase in [25(OH)D] attributable to vitamin D3 supplementation may vary according to common genetic differences in vitamin D 25-hydroxylase (CYP2R1), 24-hydroxylase (CYP24A1), and the vitamin D receptor (VDR) genes."
— Barry EL et al. Genetic variants in CYP2R1, CYP24A1, and VDR modify the efficacy of vitamin D3 supplementation for increasing serum 25-hydroxyvitamin D levels in a randomized controlled trial. J Clin Endocrinol Metab. 2014. doi:10.1210/jc.2014-1389
Note carefully what that does and does not license. It says genotype modifies how much your blood level rises on a fixed dose — a statistical effect measured across a trial population. It does not provide a validated rule for translating your genotype into a starting dose, a target level, or a monitoring schedule. No such rule has been shown to produce better outcomes than the far simpler alternative: measure the level, adjust, measure again.
How to Actually Get Your Vitamin D Right
Since genotype does not set the dose, here is what does.
Start from established intake recommendations. The Institute of Medicine's review set Recommended Dietary Allowances for vitamin D of 600 IU/day for ages 1-70 and 800 IU/day for ages 71 and older, corresponding to a serum 25(OH)D level of at least 20 ng/mL (50 nmol/L), and covering the requirements of at least 97.5% of the population. These were derived assuming minimal sun exposure.
Resist the pull toward ever-higher targets. The same review found that higher values "were not consistently associated with greater benefit, and for some outcomes U-shaped associations were observed, with risks at both low and high levels." It also concluded that the prevalence of vitamin D inadequacy in North America has been overestimated. The popular 40-60 ng/mL "optimal range" circulating in supplement content does not come from this evidence base.
Measure rather than infer. A 25(OH)D blood test costs little and answers directly what genotype only gestures at. If you are supplementing to correct a documented low level, retesting after roughly 8-12 weeks shows whether your dose is doing the job — and that empirical answer already incorporates every genetic factor affecting you, known and unknown, without needing to identify any of them.
Bring persistent non-response to a clinician. If your level stays low on consistent supplementation, that is worth investigating — malabsorption, medication interactions, body composition and adherence are all more common explanations than a rare genetic cause, and a doctor can sort through them.
| Question | What answers it |
|---|---|
| How much vitamin D do I need? | Established intake recommendations, then your measured 25(OH)D |
| Am I deficient? | A 25(OH)D blood test |
| Is my dose working? | A repeat 25(OH)D test after 8-12 weeks |
| Should I take more because of my VDR genotype? | No — these variants do not predict bone outcomes or set a dose |
Sun Exposure and Vitamin D Synthesis
Skin synthesis is a genuine and substantial source of vitamin D, and the factors that govern it are well understood — none of them are your VDR genotype.
UVB intensity is what matters, and it varies with latitude, season, and time of day. Above roughly 37° N, winter sunlight produces very little vitamin D regardless of how long you stay outside. Melanin meaningfully reduces cutaneous synthesis, which is why people with darker skin generally need longer exposure or more reliable dietary and supplemental intake to reach the same level. Age reduces synthetic capacity as well, since skin 7-dehydrocholesterol declines over time.
The unavoidable tension is that UVB exposure carries skin cancer risk, which is precisely why the IOM derived its intake recommendations under assumptions of minimal sun exposure rather than treating sunlight as the primary strategy. Supplementation is the controllable variable; sun exposure is not something to titrate against a genotype.
Cofactors: What Is Solid and What Is Marketing
Magnesium is a genuine cofactor for the enzymes involved in vitamin D metabolism, and severe magnesium deficiency can impair vitamin D handling. That is a real biochemical relationship. It does not follow that everyone supplementing vitamin D needs added magnesium, and meeting magnesium requirements through diet is reasonable for most people.
Vitamin K2 is frequently sold as an essential vitamin D partner on the theory that it directs calcium into bone rather than soft tissue. The mechanism is plausible and there is ongoing research, but the clinical evidence for routine co-supplementation in people without a specific deficiency is limited. Treat it as an open question rather than a requirement.
Calcium intake genuinely interacts with vitamin D for bone health, and the IOM issued recommendations for both together for exactly that reason.
What none of these cofactors do is rescue a genotype-based dosing scheme that has no outcome evidence behind it.
FAQ: Vitamin D Genetics and the VDR Gene
Q: Does my VDR genotype tell me how much vitamin D to take?
No. The largest study of these variants — 26,242 participants — found no association between the FokI, BsmI, ApaI and TaqI polymorphisms and either bone mineral density or fracture risk. Since these are the outcomes vitamin D supplementation is best evidenced for, variants that do not predict them cannot sensibly set your dose. Your measured 25(OH)D level is the number that guides supplementation.
Q: What do FokI, BsmI, ApaI and TaqI actually do?
FokI (rs2228570) alters a start codon, producing a receptor protein of either 424 or 427 amino acids — a real molecular difference. BsmI (rs1544410), ApaI (rs7975232) and TaqI (rs731236) lie near the 3' end of the gene and do not change the protein sequence. Whatever functional consequences they may have, they did not translate into measurable differences in bone density or fractures at a sample size where such differences would have been detectable.
Q: Then why does so much content assign doses by VDR genotype?
Because the older literature contains many small studies with positive findings, and small candidate-gene studies of this era produced a great deal of noise that did not survive replication. Once individual-level data from tens of thousands of participants were pooled, the effects collapsed toward zero. Content built on the earlier papers has outlived the evidence that supported it.
Q: Does genetics affect vitamin D at all?
Yes — but at different genes and for a different outcome. Genome-wide studies in tens of thousands of people implicate GC (the vitamin D binding protein), CYP2R1 (liver hydroxylation), DHCR7 (skin precursor synthesis) and CYP24A1 (breakdown) in determining circulating 25(OH)D. A randomized trial also found that the rise in 25(OH)D from supplementation varied by genotypes near CYP2R1, CYP24A1 and VDR. That is a population-level statistical effect on blood levels, not a personal dosing algorithm.
Q: What 25(OH)D level should I aim for?
The IOM concluded that a serum level of at least 20 ng/mL (50 nmol/L) meets the requirements of at least 97.5% of the population for bone health, corresponding to 600 IU/day for ages 1-70 and 800 IU/day for 71 and older. Higher targets were not consistently associated with greater benefit, and some outcomes showed U-shaped risk. Clinical practice varies, and if you have osteoporosis, malabsorption, or another specific condition, your clinician may work to a different target for reasons specific to you.
Q: Why am I still deficient despite supplementing?
Look at the ordinary explanations first, because they are far more common than genetic ones: inconsistent adherence, a dose too low for your starting point, malabsorption, medications that accelerate vitamin D metabolism, and higher body weight (vitamin D distributes into adipose tissue, so more is needed to raise the serum level). Genetic variation in CYP2R1 or CYP24A1 can contribute, but it does not change the response, which is to test, adjust, and retest.
Q: Should I take calcifediol instead of D3 because of my genetics?
Not on the basis of a consumer genotype. Calcifediol (25-hydroxyvitamin D) does bypass the liver hydroxylation step and raises serum 25(OH)D faster than D3, which is why it is used in specific clinical situations such as significant liver disease. It is a prescription decision made on clinical grounds, not a genotype-driven upgrade.
Q: Can vitamin D be harmful at high doses?
Yes. Vitamin D is fat-soluble and accumulates, and excessive supplementation can cause hypercalcemia. The IOM review noted U-shaped associations for some outcomes, with risks at both low and high levels. This is the practical hazard in genotype-based dosing content: it routinely recommends doses well above established intake levels on the basis of variants that predict nothing.
Q: Does ethnic background affect my vitamin D needs?
Skin pigmentation genuinely affects cutaneous synthesis — melanin absorbs UVB, so more exposure is required to produce the same amount of vitamin D, which contributes to higher rates of low 25(OH)D among people with darker skin at higher latitudes. This is a straightforward consequence of skin biology, and it is a reason to measure your level rather than to look up a VDR genotype.
Q: Is there any point in knowing my VDR variants?
As biology, they are interesting, and knowing what your raw data contains is worthwhile. As a basis for action, no — and that is a useful thing to know, because it stops you buying a dosing protocol built on them. The most valuable output of a VDR readout is an accurate statement of what it does not tell you.
Conclusion
Vitamin D genetics is a field where the popular story ran well ahead of the evidence and never came back. The four VDR polymorphisms at the centre of nearly every genotype-based dosing scheme were tested against bone density and fractures in 26,242 people and found unassociated with both.
Genetics still matters to vitamin D, but at other genes and for a narrower outcome: GC, CYP2R1, DHCR7 and CYP24A1 influence how much 25(OH)D circulates, and genotype modifies how much your level rises on a given dose. Neither finding yields a validated personal dosing rule, and neither needs to — because the blood test that would confirm any such rule is the same one that makes it unnecessary.
The practical path is unglamorous and works: follow established intake recommendations, measure your 25(OH)D, adjust if it is low, retest to confirm, and take persistent non-response to a clinician. Your genotype is worth understanding. It is not worth dosing by.
📋 Educational Content Disclaimer
This article provides educational information about genetic variants and is not intended as medical advice. Always consult qualified healthcare providers for personalized medical guidance. Genetic information should be interpreted alongside medical history and professional assessment.